input_gpio: Fix not using latest pin state on pm resume

When the device was suspended and the pin level changed during
that time, the pin level of course isn't updated in the pins cb_data.
Once the device is resumed, this leads to potentially having
a wrong value in the pin state data leading to swallowing the first
event due to comparing the stored level vs. the new level before
reporting.

Also added some `const`s and deleted an unused struct element.

Signed-off-by: Marcel Krüger <marcel@mkgr.dev>